When making deliveries from a semi-trailer, it is necessary to provide some type of unloading platform if an operator is to enter the semi-trailer and carry goods therefrom to a receiving station. Power lift tailgates for semi-trailers are known to be permanently provided on a vehicle. The tailgates are power operated and adjustable in height. If a power lift tailgate is unavailable, an operator would climb into the semi-trailer through the side door and move goods to the door, then jump to the ground, and carry goods from the side door of the semi-trailer. An alternate arrangement was to have an unloading platform and ramp located at each receiving station so that an operator could set up the platform adjacent to the semi-trailer after arriving at a receiving station and use the ramp and platform to help unload the semi-trailer.
U.S. Pat. No. 3,599,810 to Wanko discloses a load-carrying vehicle having a supporting frame mounted below a load-carrying bed. A loading platform is provided which includes a slidable frame mounted in the supporting frame for movement between extended and withdrawn positions. Ground support castors support the slidable frame, which extends beyond one side of the load-carrying vehicle. The platform is connected to a mounting assembly, which is fixed to the trailer. The platform only extends from one side of the vehicle and is used only in combination with the vehicle to which it is permanently fixed.
U.S. Pat. No. 3,743,121 to Langer discloses an unloading chute assembly and means for detachably carrying the assembly on a vehicle. A hydraulic loading chute is carried by a semi-trailer so that it is readily available for unloading the trailer at its destination. Support legs and their attached wheels are lowered by a hydraulic cylinder. When fully lowered and locked, the chute will clear the support brackets and be moved by a hydraulic cylinder to a position of use.
Other patents related to this field include U.S. Pat. Nos. 2,457,380 to Kelberer; 2,788,137 to Harkness; 4,084,714 to Williams; and 4,131,209 to Manning.